Conventional recording heads for linear tape drives have small transducers incorporated into a large head assembly to span the full width of the tape. For recording heads fabricated using thin film wafer technology, this requires that the head either be fabricated individually on a wafer which is at least as wide as the recording tape and lapped individually to the proper shape, or be fabricated as a small part and assembled with larger pieces and the full assembly lapped individually to the proper shape.
The conventional shape of a tape head comprises a cylindrical or complex contour which is critical in maintaining the moving tape at the desired head to transducer spacing (called "contact" or "near contact" recording). The contact, or near contact, spacing is maintained by controlling the contour shape to "bleed", "skive" or "scrape" the boundary layer of air carried by the tape away before encountering the transducer to prevent the tape from "flying", or losing contact with the transducer.
The spacing between the magnetic head and the magnetic tape is crucial so that the recording gap of the transducer, which is the source of the magnetic recording flux, is in intimate or near contact with the tape to effect efficient signal transfer for recording. The spacing is also crucial so that the playback element is in intimate or near contact with the tape to provide effective coupling of the magnetic field from the tape to the playback element.
The full width of the tape in the prior art is contacted by the head assembly to prevent steering the moving tape as the head assembly is moved to access different data tracks. In addition, when a short span head is near an edge of the tape, the tape, without support, tends to lift from the head as the result of upward flex curvature as it travels over the protruding head. Thus, a wide head is used to provide support for the tape when the recording element is positioned near an edge of the tape. Even with full width support, there is an anticlastic bending effect that tends to lift the tape off the head near the edge of the tape.
FIG. 1 illustrates a conventional linear tape drive recording head 10. A small transducer 11 is incorporated into a large unit 12 to span the full width of the tape 13. FIG. 2 illustrates an example of one method of fabricating a conventional linear tape drive recording head of FIG. 1 using thin film wafer technology. In FIG. 2a, an individual chip 14 is assembled with wings 15 and 16 and closure 17 and glued together to form a full assembly which is shown in an end view in FIG. 2b. A portion of the top surface of the full assembly is then ground away to form the assembly shown in FIG. 2c, leaving a rooftop 18. The entire assembly is then individually lapped to the proper depth so as to attain the final stripe and throat heights for the magnetic transducer and to attain the desired contour 19 as shown in FIG. 2d. The resultant assembly is illustrated in FIG. 2e.
The conventional shape of FIG. 2 comprises a cylindrical or complex contour which is critical in maintaining the moving tape in contact with the transducer, as described above. The full width contour of FIGS. 1 and 2 serves three purposes. 1) It prevents tape steering as the recording element is moved to access different data tracks. 2) It provides support for the tape as the head is positioned near the edge of the tape 13. And 3) It prevents the edges of the chip 14 from damaging the tape. 13.
The contour of the head must also allow a low tension on the tape so as to not distort the tape. Typically, the contour is designed with a small radius 19 in FIG. 2d so the pressure on the head, which is proportional to the tape tension per unit width divided by the radius (T/wR), is high with tensions low enough not to excessively distort the tape. However, the contour of the head must be such that the pressure of the tape on the transducer is not so high that the surface of the transducer wears excessively.
Such full width heads are often provided with "outriggers" to maintain a small wrap angle over the recording elements of the head even though the wrap angle over the outriggers can change with different cartridges inserted into the tape drive. A change in wrap angle over the portion of the head containing the recording elements can lead to air entrainment and excessive flying height of the tape.
Like the head assembly, the outriggers must also be the full width of the tape in order to prevent distortion of the tape. Often, the outriggers must also be lapped to a contour which is coordinated with the contour of the head assembly.
Individual lapping of the tape head assembly and of the corresponding outriggers, especially to a contour, is very expensive and is a major contributor to the manufacturing cost of the tape head.
Partial span recording heads are used in helical scan tape recording and in floppy disks. They are individually assembled and then provided with a spherical or elliptical contour. Such heads have not been used in linear tape recorders due to the need for tape edge support and a requirement for substantial tape tension or contact pressure to maintain contact with the head. In addition, it is difficult to provide such a contour when a multiplicity of recording elements are required in the head.
U.S. Pat. No. 4,123,791, Rotter et al., describes a single element narrow tape head positioned between outrigger bars of 0.25 inch radius with radial centers 0.4 inch apart. An additional pair of stub outriggers aligned in the direction of tape travel, having the same shape as the head and spaced 25 to 30 mils on either side of the head, were required to support the edge of the tape. The narrow tape head and stub outriggers were required to allow the splitting and passage of the boundary layer of air.